This invention relates generally to wireless communications and more particularly to demodulation within a wireless radio receiver.
The use of wireless communication for in-home and/or in-building networks and/or point to point communications is increasing in popularity and spawning relatively new standards including, but not limited to Bluetooth, IEEE 802.11a, IEEE 802.11b, et cetera. As is known for wireless communications, data is modulated on to at least one RF (radio frequency) carrier frequency and transmitted as a RF modulated signal by a radio transmitter. A radio receiver receives the RF modulated signal and demodulates it to recapture the data.
As is further known, there are a variety of modulation/demodulation protocols that may be used for wireless communications. Such modulation and demodulation protocols include amplitude modulation (AM), frequency modulation (FM), amplitude shift-keying (ASK), frequency shift-keying (FSK), phase shift-keying (PSK), orthogonal frequency division multiplexing (OFDM), or variations thereof. As is also known, Bluetooth utilizes an FSK modulation/demodulation protocol while IEEE 802.11a and IEEE 802.11b utilize an PSK and/or OFDM modulation/demodulation protocol.
Regardless of the particular modulation/demodulation protocol, a radio receiver generally includes an antenna section, a band-pass filter, a low noise amplifier, an intermediate frequency (IF) stage, and a demodulator. In operation, the antenna section receives RF modulated signals and provides them to the band-pass filter, which passes RF signals of interest to the low noise amplifier. The low noise amplifier amplifies the received RF signals and provides the amplified RF signals of interest to the IF stage. The IF stage includes one or more local oscillators, one or more mixers, and one or more adders to step-down the frequency of the RF signals to an intermediate frequency or base-band frequency. The IF stage provides the IF or base-band signal to the demodulator which, based on the modulation/demodulation protocol, recaptures the data.
A demodulator may be implemented using analog and/or digital circuitry. While fully digital demodulators are known and better suited for use in an integrated circuit radio receiver than analog demodulators due to their reduced sensitivity to noise, digital demodulators are complex, are integrated circuit real estate intensive, and relatively costly. Another issue with current digital demodulators is that they consume a relatively large amount of power. For example, a demodulator that uses a local oscillator to convert signals to base-band requires up to 5 milliamps at 3 volts. If the demodulator processes data at the intermediate frequency, the power requirements are 3 milliamps at 3 volts.
Therefore, a need exists for a low power, reliable and reduced complexity digital demodulator.